What you’re looking for is genealogy software. You’ve got me curious about this as well now, hadn’t thought about it before. I’m seeing some recommendations online for Gramps Web, don’t know if it’s a perfect fit but might be a good starting point.

This is really awesome! I was just about to start looking for something like this, so great timing. Going to get this up on my Unraid server tomorrow and play around with it

It’s not a calendar, it’s an appointment scheduler